The present disclosure relates to a flat-type display device. As image display devices which will possibly replace cathode-ray tubes (CRTs) currently widely spread, flat (flat panel type) display devices are vigorously studied. Examples of the flat display devices include a liquid crystal display (LCD), an electroluminescence display (ELD), and a plasma display (PDP). In addition, flat display devices having incorporated therein a cathode panel having an electron emission device are also developed. As electron emission devices, a cold cathode field emission device, a metal/insulating film/metal element (also called an MIM element), and a surface conductive-type electron emission device are known, and a flat display device having incorporated therein a cathode panel having the above electron emission device composed of a cold cathode electron source has attracted attention since it advantageously achieves color display with high resolution and high luminance and causes low power consumption.
A cold cathode field emission display device (hereinafter, frequently referred to simply as “display device”) is a flat display device having incorporated therein a cold cathode field emission device as an electron emission device. This type of display device generally has a structure having a cathode panel CP and an anode panel AP disposed so that they face each other through a high-vacuum space, and joined together at their edges through a joint member. The cathode panel CP has a plurality of cold cathode field emitter elements (hereinafter, frequently referred to simply as “field emitter element(s)”), and the anode panel AP has a fluorescent region with which electrons emitted from the field emitter elements collide and which are excited to emit light. The cathode panel CP has electron emitter areas arrayed in a two-dimensional matrix form and corresponding to respective subpixels, wherein each electron emitter area has formed one or a plurality of field emission devices. Examples of field emitter elements include those of Spindt type, flattened type, edge type, or flat type.
A schematic fragmentary end view of a display device having a Spindt-type field emission device as an example is shown in FIG. 10, and a partial, schematic exploded perspective view of a cathode panel CP and an anode panel AP separated from each other is shown in FIG. 12. The Spindt-type field emission device constituting the display device includes a cathode electrode 11, an insulating layer 12, a gate electrode 13, openings 14, and a conical electron emitter 15. Herein, the cathode electrode 11 is formed on a support 10. The insulating layer 12 is formed on the support 10 and the cathode electrode 11. The gate electrode 13 is formed on the insulating layer 12. The openings 14 are formed in the gate electrode 13 and insulating layer 12, in which a first opening 14A formed in the gate electrode 13 and a second opening 14B formed in the insulating layer 12. The conical electron emitter 15 is formed on the cathode electrode 11 at the bottom of each opening 14.
A schematic fragmentary end view of a display device having a so-called flattened field emission device having a substantially planar electron emitter 15A is shown in FIG. 11. This field emission device is similar to the Spindt-type field emission device as described above, and is different in having an electron emitter 15A formed on the cathode electrode 11 at the bottom of each opening 14, instead of the electron emitter 15. The electron emitter 15A is composed of, for example, a number of carbon nanotubes, part of which is buried in the matrix.
In these display devices, the cathode electrode 11 is in the form of a strip extending in a first direction (corresponding to the X direction shown in the figures), and the gate electrode 13 is in the form of a strip extending in a second direction (corresponding to the Y direction shown in the figures) different from the first direction (X direction). Generally, the cathode electrode 11 and the gate electrode 13 are formed in strips in respective directions such that the images from the electrodes 11, 13 cross at a right angle. An area where the strip-form cathode electrode 11 and the strip-form gate electrode 13 overlap is an electron emitter area EA, and corresponds to one subpixel. The electron emitter areas EA are generally arrayed in a two-dimensional matrix form in an effective region of the cathode panel CP. The effective region herein means a display area at the center having a practical function of the flat display device, i.e., display function, wherein an ineffective region is present on the outside of the effective region and in the form of a frame surrounding the effective region.
On the other hand, the anode panel AP has a structure including fluorescent regions 22 having a predetermined pattern formed on a substrate 20 wherein the fluorescent regions 22 are covered with an anode electrode 24. The fluorescent regions 22 include, specifically, a red light-emitting fluorescent region 22R, a green light-emitting fluorescent region 22G, and a blue light-emitting fluorescent region 22B. A light absorbing layer (black matrix) 23 composed of a light absorbing material, such as carbon, is buried between the fluorescent regions 22 to prevent the occurrence of color mixing in the display image, optical cross talk. The barrier 21 has a flat form of lattice-like form, that is, form of parallel crosses, surrounding one subpixel or a fluorescent region. In the figure, a reference numeral 40 designates a spacer, a reference numeral 25 designates a spacer holder, a reference numeral 26 designates a joint member, a reference numeral 17 designates a focusing electrode, and a reference numeral 16 designates an interlayer dielectric layer. In FIGS. 11 and 12, the barrier, spacer, spacer holder, and focusing electrode are not shown.
One subpixel is composed of the electron emitter area EA on the cathode panel side, and the fluorescent region 22 on the anode panel side opposite (facing) the above electron emitter area EA. The pixels on the order of, e.g., several hundred thousand to several million are arrayed in the effective region. In the display device making color display, one pixel is composed of an assembly of a red light-emitting subpixel, a green light-emitting subpixel, and a blue light-emitting subpixel.
The electrons emitted from the electron emitter areas EA collide with the anode electrode 24 and pass through the anode electrode 24, and collide with the fluorescent regions 22, so that the fluorescent regions 22 are excited to emit light. Part of the electrons, which have collided with the anode electrode 24 or fluorescent regions 22, bounce in the direction from the anode panel AP to the cathode panel CP. Further, the collision of the electrons with the fluorescent regions 22 causes the fluorescent regions 22 to emit secondary electrons in the direction to the cathode panel CP. The bouncing electrons and the secondary electrons are collectively referred to as “backscattering electrons”.
By the way, it is known that, with respect to the lowering of the contrast due to the backscattering electrons on the cold cathode field emission display device is remarkable, as compared to a case of a cathode-ray tube. Specifically, backscattering electrons collide with, for example, the adjacent fluorescent region to cause light emission from an undesired fluorescent region, thus lowering the contrast. Examples of reasons that such a phenomenon is likely to occur in the cold cathode field emission display device include:
(1) a fact that the potential gradient in the space between the anode panel AP and the cathode panel CP is as large as about 20 to 70 times that in the cathode-ray tube;
(2) a fact that irradiation of electrons to the fluorescent regions is conducted in a linear sequential mode, and therefore a period of time during which the electrons collide with the fluorescent regions is long, namely, the total number of electrons which collide with the fluorescent regions is large and, consequently, the absolute value of backscattering electrons is large; and
(3) a fact that the cold cathode field emission display device does not have a color identification mechanism which contributes to absorption of the scattering electrons and which is inherent in a cathode-ray tube that has been subjected to surface treatment, for example, oxide film treatment.
A technique for avoiding the adverse effect of the backscattering electrons, in which, for example, a carbon layer is formed on the anode electrode composed of, e.g., an aluminum layer, has been disclosed in Japanese Patent Application Publication (KOKAI) No. Hei 10-321169. The carbon layer has a lower scattering coefficient for primary electrons than that of the aluminum layer, and hence it is believed that the carbon layer reduces the number of electrons which enter the fluorescent regions to scatter.
However, this technique has the following problem. After the carbon layer is formed on the anode electrode composed of an aluminum layer, the anode panel having the carbon layer is processed through various thermal steps. The carbon layer is adversely affected by heat shrinkage due to heating and cooling or the heating atmosphere in the thermal steps, so that the carbon layer is partially or completely peeled off the aluminum layer or a crack is caused in the carbon layer. Such a phenomenon results in particles or a sharp portion on the carbon layer, so that the application of a high voltage to the anode electrode induces discharge, thus lowering the reliability or shortening the life of the display device.
Additional features and advantages are described herein, and will be apparent from, the following Detailed Description and the figures.